Since at least as early as the mid-1960's, scientific and economic forecasters have been predicting an approaching era of diminishing availability of petrochemical resources to produce the energy and chemical materials needed by industrialized societies. On one hand, discoveries of new petroleum reserves and new petroleum production technologies (e.g., deep-water, off-shore drilling) have staved off an economically catastrophic shortage of crude oil. On the other hand, rapidly industrializing national economies (most notably China and India), coupled with political instability in petroleum-producing regions (most notably the middle east, Nigeria, and Venezuela), have pushed oil prices to record levels. In early 2006, the price of a barrel of crude oil topped $70 for the first time in history. Environmental, ecological, and political considerations have also effectively made certain proven reserves of petroleum off-limits to commercial exploitation. For example, production of petroleum from proven reserves in the Artic National Wildlife Refuge in Alaska has been (and for the foreseeable future, will continue to be) blocked by federal and state legislation to preserve this unique natural landscape from human encroachment.
The rippling effect of high crude oil prices on national economies is profound. Not only are gasoline and diesel the principal transportation fuels worldwide, crude petroleum also yields a vast array of chemicals that are feedstocks for an equally vast array of products, from plastics to pesticides. Thus, high crude oil prices spur worldwide inflation as producers pass on their increased costs of production to consumers.
The economic difficulties caused by increasing demand coupled with diminishing supply is driving efforts to develop alternative and sustainable ways to meet energy and raw material needs. The Roadmap for Biomass Technologies in the United States (U.S. Department of Energy, Accession No. ADA436527, December 2002), authored by 26 leading experts, has predicted a gradual shift from a petroleum-based economy to a more carbohydrate dependent economy. This official document predicts that by 2030, 20% of transportation fuel and 25% of chemicals consumed in the United States will be produced from biomass. Such a shift away from petroleum-based technologies requires developing innovative, low-cost separation and depolymerization processing technologies to break down the highly oxygen-functionalized, polysaccharide molecules found in raw biomass, to yield useful bio-derived materials and fuels. In short, abundant biomass resources can provide alternative routes for a sustainable supply of both transportation fuels and valuable intermediates (e.g., alcohols, aldehydes, ketones, carboxylic acid, esters) for production of drugs and polymeric materials. However, unless these alternative routes can be implemented at a production cost roughly comparable to the corresponding production cost when using petroleum feedstocks, the transition will inevitably be accompanied by severe economic dislocations. It is not enough that the transition can be accomplished; to avoid economic upheaval, the transition must be accomplished in an economically feasible fashion.
Furan derivatives (such as furfural (Fur) and 5-hydroxymethylfurfural (HMF)) derived from renewable biomass resources have potential as substitutes for petroleum-based building blocks used to produce plastics and fine chemicals. For example, HMF can be converted to 2,5-furandicarboxylic acid (FDCA) by selective oxidation; FDCA can be used as a replacement for terephthalic acid in the production of polyesters such as polyethyleneterephthalate (PET) and polybutyleneterephthalate (PBT). Reducing HMF leads to products such as 2,5-dihydroxymethylfuran and 2,5-bis(hydroxymethyl)tetrahydrofuran, which can function as the alcohol components in the production of polyesters (thereby leading to completely biomass-derived polymers when combined with FDCA). Additionally, disubstituted furan derivates obtained from HMF serve as an important component of pharmacologically active compounds associated with a wide spectrum of biological activities. Furfural is also a key chemical for the commercial production of furan (via catalytic decarbonylation) and tetrahydrofuran (via hydrogenation), thereby providing a biomass-based alternative to the corresponding petrochemical production route (via dehydration of 1,4-butanediol).
Furfural is primarily used in refining lubricating oil. Furfural is also used in condensation reactions with formaldehyde, phenol, acetone or urea to yield resins with excellent thermosetting properties and extreme physical strength. Methyl-tetrahydrofuran (MeTHF), a hydrogenated form of furfural, is a principal component in P-series fuel, which is developed primarily from renewable resources. (“P-series fuel” is an official designation promulgated by the U.S. Dept. of Energy for a fuel blend comprised of pentanes, ethanol, and biomass-derived MeTHF. See 10 CFR §490.)
However, as indicated by various authors, the industrial use of HMF as a chemical intermediate is currently impeded by high production costs. Perhaps because of the high cost of production, a number of U.S. and foreign patents describe methods to produce HMF. See, for example, U.S. Pat. Nos. 2,750,394 (to Peniston); 2,917,520 (to Cope); 2,929,823 (to Garber); 3,118,912 (to Smith); 4,339,387 (to Fleche et al.); 4,590,283 (to Gaset et al.); and 4,740,605 (to Rapp). In the foreign patent literature, see GB 591,858; GB 600,871; and GB 876,463, all of which were published in English. See also FR 2,663,933; FR 2,664,273; FR 2,669,635; and CA 2,097,812, all of which were published in French.
Producing furfural from biomass requires raw materials rich in pentosan, such as corncobs, oat hulls, bagasse, and certain woods (like beech). Even today, most furfural production plants employ batch processing using the original, acid-catalyzed Quaker Oats technology (first implemented in 1921 by Quaker Oats in Cedar Rapids, Iowa as a means to realize value from the tons of oat hulls remaining after making rolled oats). (For an exhaustive history on the production of furfural, see K. J. Zeitsch, “The Chemistry and Technology of Furfural and its Many By-Products,” Elsevier, Sugar Series, No. 13, © 2000, Elsevier Science B. V.) This batch processing results in yields less than 50%, and also requires a large amount of high-pressure steam. The process also generates a significant amount of effluent.
Various researchers have tried dehydration of xylose into furfural using acid catalysts such as mineral acids, zeolites, acid-functionalized Mobile crystalline materials (MCM's) and heteropolyacids. Moreau et. al. has conducted the reaction in a batch mode using H-form faujasites and a H-mordenite catalyst, at 170° C., in a solvent mixture of water and methylisobutylketone (MIBK) or toluene (1:3 by vol) with selectivities ranging from 70-96% (in toluene) and 50-60% (in MIBK) but at low conversions. Dias et al. showed that a sulfonic acid-modified MCM-41-type catalyst displayed fairly high selectivity to furfural (˜82%) at high xylose conversion (>90%) with toluene as the extracting solvent for the reactions carried out 140° C. In the patent literature, see, for example, U.S. Pat. Nos. 4,533,743 (to Medeiros et al.); 4,912,237 (to Zeitsch); 4,971,657 (to Avignon et al.), and 6,743,928 (to Zeitsch).
Abundant biomass resources are a promising sustainable supply of valuable intermediates (e.g., alcohols, aldehydes, ketones, carboxylic acids) to the chemical industry for producing drugs and polymeric materials. In this context, the high content of oxygenated functional groups in carbohydrates, the dominant compounds in biomass, is an advantage. (Which is in contrast to the drawbacks of such functionality for the conversion of carbohydrates to fuels.) However, there remains a long-felt and unmet need for efficient processes to selectively remove excess functional groups and to modify other functional groups to create commercially desirable products from biomass.